Process for generating a common time base for a system with distributed computing units

Abstract

In a process for operating computing units in communication with each other by serial data transfer over a data bus, each unit having its own clock generating system and the computing units exchanging timing information over the data bus, provision is made to generate a system timing using the transfer protocol that is valid for the system. For this purpose, a time registration start signal is first fed into the data bus; thereupon, each computing unit stores its own time value upon identification of the time registration start signal, transfers the stored own time value at a later moment in time to the other computing units and stores the time values received from the other computing units. Each computing unit then compares its own stored time value with the stored time values of the other computing units and calculates the present time value of the other computing units taking into account its own present time value. Each computing node can thus very accurately ascertain the relationship between its local time base and the local time bases of the other computing nodes, or a reference node, without having to adjust or correct the local time base.

I claim: 
     
       1. Process for operating computing units in communication with each other by serial data transfer over a data bus, with each computing unit having its own clock generating system and the computing units exchanging timing information over the data bus, characterized by the steps of: a) feeding a time registration start signal into the data bus;   b) each computing unit storing its own time value upon identification of the time registration start signal;   c) at least one computing unit selected as reference computing unit transferring its own stored time value to the other computing units at a later moment in time; and each computing unit:   d) storing the time values received from the other computing units;   e) comparing its own stored time value with the stored time values of the other computing units; and   f) calculating the present time values of the other computing units while taking into account its own present time value.   
     
     
       2. Process according to claim 1, characterized by the steps of: a) feeding two or more time registration start signals into the data bus at successive moments in time;   b) each computing unit storing its corresponding own time value upon identification of each time registration start signal;   c) at least one computing unit selected as reference computing unit transferring its own stored time values to the other computing units at a later moment in time or at later moments in time; and each computing unit:   d) storing the time values received from the other computing units;   e) comparing its own time values with the stored time values of the other computing units; and   f) calculating the present time values of the other computing units while taking into account its own present time value.   
     
     
       3. Process according to claim 1 or claim 2, characterized by the step of feeding the time registration start signal or the time registration start signals into the data bus by one of the computing units. 
     
     
       4. Process according to claim 1 or claim 2, characterized by the step of using a characteristic part of a data series as the time registration start signal. 
     
     
       5. Process according to claim 4, characterized by the step of providing verifying data for the time registration start signal, and providing the data series with a time registration start signal. 
     
     
       6. Process according to claim 5, characterized by the step of each computing unit deleting its own time value, stored when a time registration start signal appeared on the data bus, if the computing unit does not recognize verifying data belonging to the time registration start signal. 
     
     
       7. Process according to claim 4, characterized by the step of using a first pulse edge of a data series as a time registration start signal. 
     
     
       8. Process according to claim 4, characterized by the steps of, in the case of a longer data series, synchronizing hardware, of the pulse raster generated by the receiving computing unit, with a synchronizing signal contained in the data series, for bit identification of the received data, and using the synchronization signal as the time registration start signal.